An imaging lens used for an imaging device includes a plurality of lens groups, and is configured such that distances between lens groups in an optical axis direction vary so that functions such as focusing, zooming namely continuous variation of focal length and collapse are performed. In particular, in an imaging lens equipped with a zoom function or a collapse function or both of the functions, a movement distance in an optical axis direction of a lens groups is long, and a structure of a lens barrel is complex.
Recently, a photographing device such as a digital camera, is requested to have a high performance by which a high quality image can be obtained while having the zoom function, and is requested to be compact for improving the convenience when carrying, and these needs are met by the progress of technological developments. For example, use of a collapsible camera has increased due to a collapsible lens barrel, and is effective to meet the need for compactness. As a mechanism to move a lens group to carry out a collapse function or a zoom function, such a mechanism in which a rotation cylinder is retained by a fixed cylinder, and a lens frame moves backward or forward in an optical axis direction when the rotation cylinder is rotated relative to the fixed cylinder through a cam engagement or a helicoid engagement is usually employed. In a typical mechanism, a fixed cylinder is engaged with a rotation cylinder through a cam, and the rotation cylinder is configured to move backward or forward in an optical axis direction of a lens following a cam groove while rotating centered on the optical axis of the lens, and a straight guide cylinder which is configured to be rotatable relative to the rotation cylinder inside the rotation cylinder and move straight integrally with the rotation cylinder in the optical axis direction is provided, and a lens frame which retains the lens is retained inside the straight guide cylinder.
The lens frame has a cam follower, and the cam follower penetrates through a straight groove extended in an optical axis direction of the straight guide cylinder and is engaged with a cam groove provided at an inner face of the rotation cylinder. When the rotation cylinder rotates, the lens is capable of moving to any position within a movement range in the optical axis direction without rotating along a shape of the cam groove. The rotation cylinder and the straight guide cylinder are engaged for example by engaging a rotation key which is provided at the straight guide cylinder and projects radially with a rotation groove provided at the inner face of the rotation cylinder. According to this structure, the straight guide cylinder can move in the optical axis direction integrally with the rotation cylinder while rotating around the optical axis relative to the rotation cylinder.
A lens barrel is requested in which optical axes of lenses are capable of aligning to maintain an excellent imaging performance. However, it becomes difficult to align the optical axes when a number of driving members which drive the lens increases, and a higher accuracy of the optical axes alignment is requested when the lens barrel is made more and more compact. A structure or a method for aligning optical axes of lenses includes the following: a lens or a lens group having a plurality of lenses is moved in a plane perpendicular to an optical axis and each optical axis of the lenses is aligned; and each of the lenses is tilted to align the optical axes of the lenses.
As a method of tilt adjustment of a lens frame, JP 2006-3837 A discloses a method in which a tilt adjusting washer is selectively inserted between the lens frame and its retaining frame to make adjustments. According to this method, there is a drawback in that it is necessary to confirm the tilt of the lens frame while changing the washer, and assembling and the adjustment become troublesome.
JP 2005-70417 A discloses a lens adjusting device in which a lens frame has a sphere shaped outer circumference, a retaining frame which retains the lens frame and has a sphere shaped inner circumference matching the sphere shape outer circumference of the lens frame, and the lens frame is moved along these sphere shapes. According to this invention, it is necessary to match each sphere shape precisely, the processing of components is extremely difficult, and further, since the lens frame is retained by the sphere shaped structure, it is a weak structure to impact as the lens frame shifts when a load such as the impact is applied.
JP 2003-279823 A discloses a tilt adjusting mechanism in which a lens frame is biased and supported in an optical axis direction by a spring in a lens barrel frame, a rotation plate is disposed between the lens barrel frame and the lens frame, a plurality of convex parts with different heights are formed on a surface of the rotation board facing the lens frame, a plurality of concave parts capable of receiving the plurality of convex parts are formed on the lens frame, and tilt of the lens frame is adjusted by selecting the convex part of the rotation frame which fits in the concave part of the lens frame. According to the invention, though component formation and assembling are easy, there is a drawback in that the tilt adjustment of the lens frame only can be performed step-by-step, and a minute adjustment can not be made.